Title: Initial Ionization Reaction in Matrix-Assisted Laser Desorption/Ionization

Author: Bo-Hong Liu, Olog P. Charkin, Nina Klemenko, Chiu Wen Chen, and Yi-Sheng Wang.
Journal: J. Phys. Chem. B
Year: 2010
Vol: 114,
Page: 10853-10859

• Abstract

Electron Transfer of photoelectron can precipitate other reactions in MALDI ionization.

• Introduction:

1. The mechanism of charge distribution in MALDI is not clear but important.
2. A generally accepted process of photoexcitation.
3. Summary the literature about the influence of electrons in ion formation.
4. Introduction of this work: study the step of ionization in MALDI based on previous work.

• Experiment Section

1. Description of ion source used in this experiment.
2. Introduction of sample probe of this experiment.
3. Description of laser beam used in this experiment.
4. All the compounds used in this experiment.
5. The reason for choosing S/N over 20 in this experiment.
6. The conditions given in DFT calculation.

• Results

• Mass Sepctrometric Details

1. Explain the data in figure 2 and table 1, give the conclustion that signial intensity rised up with increasing of fluence.
2. Further increase the fluence, the intensity of photoelectron will decrease.
3. Different matrix has various threshold behavior as increase of fluence, but they have the same tendency: as the increasing of fluence, the intensity of photoelectron increased.

• Theoretical Structure and Energetic Prediction

1. Various structures of DHB clusters were tested to study the trend of IP as the increasing the cluster sizes of DHB cluster.
2. Results of the test: trends of IP of each type of structure of DHB cluster as increasing of cluster sizes.
3. The trends received from different type of structure is similar: as sizes increasing, IP decreased.
4. The comparison of the structure of crystalline DHB and clusters (DHB)n.
5. All the three types of basic structure constitute the whole structure of crystalline DHB.
6. IP received in this experiment is deviated from the prediction and the reason.

• Contribution of Photoelectrons to MALDI

1. Ionization of MALDI will happen at a softer conditions than previously expected.
2. If fluence is high enough, some particles will capture electron and become negative ions and then leave solid DHB.
3. The reaction steps of DHB will be various under different laser fulence.
4. Difference between DHB and other matrix molecules in abundance of photoelectron at the same condition.

• Conclustion

The photoelectron ejected by different matrix: DHB, SA and THAP, before desorption, will precipitate other primary ionization reactions.
Initial Ionization Reaction in Matrix-Assisted Laser Desorption/Ionization